This disclosure generally relates to control of xerographic marking engines, such as copiers and laser printers.
The basic xerographic process used in a xerographic imaging device generally involves an initial step of charging a photoconductive member to a substantially uniform potential, Vcharge. The charged surface of the photoconductive member is thereafter exposed to a light image of an original document to selectively dissipate the charge thereon in selected areas irradiated by the light image. This procedure records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the document being produced. The latent image is then developed by bringing a developer material including toner particles adhering triboelectrically to carrier granules into contact with the latent image. The toner particles are attracted away from the carrier granules to the latent image, forming a toner image on the photoconductive member which may be transferred, during a process that may be referred to as a transfer stage, directly to a copy sheet or transferred to an intermediate transfer belt and subsequently transferred to a copy sheet. The copy sheet having the toner image thereon is then advanced to a fusing station for permanently affixing the toner image to the copy sheet in an image configuration.
During a transfer stage of the example xerographic process cycle, described above, an electric transfer field, hereafter referred to as a transfer field, may be applied to a transfer target to facilitate the transfer of the toner image from a transfer source to the transfer target. For example, if a toner image is to be transferred from a photoreceptor to paper, a transfer field may be applied to the paper to facilitate the transfer of the toner image to the paper; if a toner image is to be transferred from a photoreceptor to an intermediate transfer belt, a transfer field may be applied to the intermediate transfer belt to facilitate the transfer of the toner image from the photoreceptor to the intermediate transfer belt; and if a toner image is to be transferred from an intermediate transfer belt to paper, a transfer field may be applied to the paper to facilitate the transfer of the toner image from the intermediate transfer belt to the paper.
To maximize the efficiency of the toner image transfer process, i.e., the transfer efficiency, the transfer field applied to the transfer target is manually set to a value that reduces transfer associated IQ defects while keeping toner waste to a minimum. Further, the applied transfer field may be regulated to assure that the selected set point is maintained. However, such fixed transfer fields are static, or are only changed based on open loop information such as paper type or humidity, and are not automatically adjusted based on feedback measurements to maintain a desired transfer efficiency in response to variations in operational conditions and/or variations in the materials, e.g., paper type, paper humidity, toner type, toner age/condition, that may adversely affect transfer efficiency, and/or other noise. The inability to dynamically adjust xerographic process transfer fields adversely affects image quality and increases operating cost by wasting toner that otherwise would have been included in the printed xerographic output.